Hydrophilic contact lenses, which may be disposable after a single wear or short-term use, have become quite popular because of comfort and convenience. Generally, such hydrophilic contact lenses are manufactured from suitable hydrophilic polymeric materials. These materials may be, amongst others, copolymers of hydroxyethyl methacrylate containing from about 20% to 90% or more of water, depending upon the polymer composition. Generally, such hydrophilic contact lenses must be stored in a sterile aqueous solution, usually in isotonic saline solution in order to prevent dehydration and to maintain the lenses in a ready-to-wear condition. In order to maintain this high water content, hydrophilic lenses are typically immersed in a sterile, aqueous solution within a watertight package during storing, shipping, and handling processes.
The packaging of hydrophilic contact lenses in a sterile aqueous solution is well known in the contact lens manufacturing technology. There have been a variety of packages used to store hydrophilic contact lenses. In particular, so-called blister packages are widely used for the storage and dispensing of the hydrophilic contact lenses. Typically, the blister package for storing and dispensing a hydrophilic contact lens includes an injection-molded or thermoformed plastic base portion incorporating a molded cavity which is surrounded by an outstanding planar flange about the rim of the cavity. The plastic base portion is made of hydrophobic material. A flexible cover sheet is adhered to the surface of the flange so as to sealingly enclose the cavity in a generally liquid-tight mode. Within the cavity of the base portion, a hydrophilic contact lens is immersed in a sterile aqueous solution, such as an isotonic saline solution.
More recently, with the recent developments in new silicone hydrogels, soft contact lenses made of such silicon hydrogels and having hydrophilic coatings are increasing in popularity, since such lenses have high oxygen permeability, high water content, high ion permeability, all of which are required to maintain corneal health and wear comfort. Like hydrophilic contact lens, such silicone hydrogel lenses typically are already hydrated and packaged in a sterile aqueous solution and therefore can be immediately worn upon purchase, by merely removing the lens from the package, without any subsequent treatment of the lens or additional preparation by the consumer. In general, packages traditionally for hydrophilic contact lenses are used to store and dispense silicon hydrogel contact lenses. However, there are problems associated with use of traditional lens packages for storing and dispensing silicon hydrogel lenses.
Contact lenses, which are hydrated and packaged in solution, must be sterilized. Sterilization of the hydrated lenses during manufacturing and packaging is typically accomplished by autoclaving. The autoclaving process involves heating the packaging of a contact lens to a temperature of about 121° C. for approximately 20 minutes under pressure. It has been found that autoclaving of a silicone hydrogel lens packaged in a plastic package can cause deformations of a silicone hydrogel lens. Such deformations can affect the production yield of contact lenses and increase production cost.
Therefore, there is a need for a method of sterilizing silicon hydrogel contact lenses. There is also a need for improved packages for storing and dispensing silicon hydrogel contact lenses.